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Using a thicker than recommended PAG oil: really a big deal now?

Posted: Mon Apr 27, 2020 9:16 am
by Al9
Hi, really curious about this one.

I know my car's compressor, a swashplate variable design, runs on 46 weight PAG oil, even though it originally asked for a 60 weight PAG oil. Even then, some of these can be found having a label stating that the thicker RL488 oil is needed.

Ester 100 comes in between, in that viscosity wise it basically behaves like PAG 100 while cold and PAG 46 while hot, due to a lower VI.

I easily understand how and why a thicker 100 weight PAG oil, one especially laced with a serious EP package, is required in a vane compressor, and i also easily understand why, say, an older design such as the V5 requires the 150 weight PAG, however i fail to understand how using a thicker than required oil in a modern swashplate or scroll design may affect the compressor's durability and/or operation. And what about an old compressor? Could it somewhat benefit from a thicker oil charge while on its last legs?

One thing might be using the first AC oil on the shelf to make up for whatever has been recovered during the usual "top up" (improper term here, since the correct process is much more involved than that) kind of AC service, and using PAG 100 or PAG 150 instead of PAG 46 likely wouldn't impact the oil charge properties that much, but what about replacing a condenser and receiver assembly or a compressor, things that require a sizeable oil refill? What about flushing a system up and then refilling the compressor with PAG 100 instead of PAG 46? Is it going to be a big deal?

I don't think it's got to be an oil return issue, since in most automotive designs line lenght isn't an issue unless it's a dual evaporator setup. Might start becoming an issue once you switch to an application such as a dedicated dash AC system on a bus/coach.